Editing Background Music
If the video is already encoded into a single file with the instructor’s audio and the music, there is no easy way to do this, especially in a software with limited audio capabilities like Blender. There may be something you can do with a script, but advanced audio processing is not one of Blender’s strong suits. 

If the video was edited in Blender, however, and you have access to the blend file, you can go to the Video Sequence Editor, select the audio track with the music and manually turn down its volume (by pressing n on the timeline to open the properties panel).

If it was edited in another software, you’ll need to open the project in the software it was originally edited in.